Though once outliers, their ranks continue to grow among the nerds and jocks, preps and emos of America’s high schools — the heavier set kid in the sweatshirt killing another bag of chips from the vending machine.

During the past 30 years their numbers have quadrupled among teenagers as one in three U.S. children and adolescents are now overweight or obese, according to the Centers for Disease Control and Prevention. Now, researchers say such teenagers consuming a high-salt diet may experience an accelerated rate of cellular aging, in evidence shown this week at a meeting of the American Heart Association.

"Lowering sodium intake, especially if you are overweight or obese, may slow down the cellular aging process that plays an important role in the development of heart disease," lead researcher Haidong Zhu, an assistant professor of pediatrics at Georgia Regents University, said in a statement.

The protective telomeres of the chromosome naturally attenuate with age, though the process is speeded by smoking, lack of exercise, and a higher percentage of body fat. Now, Zhu has found that sodium may help to shorten telomere length at much younger ages. In the study, researchers divided 766 participants, ages 14 to 18, into low and high salt intake groups, with the former consuming 2,388 milligrams per day (mg/day) of salt on average, compared to 4,142 mg/day by the others.

Both low- and high-salt groups consumed more sodium than the 1,500 mg/day recommended by the American Heart Association.

After considering other factors affecting telomere length, Zhu and his colleagues found significantly shorter telomere length among overweight and obese teenagers consuming a higher-salt diet. Among heavier teenagers who consumed less salt, however, no such association was seen.

"Even in these relatively healthy young people, we can already see the effect of high sodium intake, suggesting that high sodium intake and obesity may act synergistically to accelerate cellular aging," Zhu said.

Overweight and obese teenagers who consume higher amounts of salt may experience this faster cellular aging for a couple of reasons, Zhu said. Teenagers with obesity experience higher levels of inflammation, which is itself associated with a speeded cellular aging process. That inflammation also increases sensitivity to salt.

"Lowering sodium intake may be an easier first step than losing weight for overweight young people who want to lower their risk of heart disease," Zhu said. "The majority of sodium in the diet comes from processed foods, so parents can help by cooking fresh meals more often and by offering fresh fruit rather than potato chips for a snack."